package com.test.utils;

import java.nio.charset.Charset;

/**
 * x^16+x^15+x^2+1
 * (1 + x^2 + x^15 + x^16)
 */
public class CRC16 {

	private static final int[] table = { 0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241, 0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440, 0xCC01, 0x0CC0, 0x0D80,
			0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40, 0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841, 0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40, 0x1E00, 0xDEC1,
			0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41, 0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641, 0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040, 0xF001,
			0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240, 0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441, 0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
			0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840, 0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41, 0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81,
			0x2C40, 0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640, 0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041, 0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1,
			0xA281, 0x6240, 0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441, 0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41, 0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900,
			0xA9C1, 0xA881, 0x6840, 0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41, 0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40, 0xB401, 0x74C0, 0x7580, 0xB541,
			0x7700, 0xB7C1, 0xB681, 0x7640, 0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041, 0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241, 0x9601, 0x56C0, 0x5780,
			0x9741, 0x5500, 0x95C1, 0x9481, 0x5440, 0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40, 0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841, 0x8801, 0x48C0,
			0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40, 0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41, 0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641, 0x8201,
			0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040, };

	private int crc;

	public int getValue() {
		return crc;
	}

	public void update(byte[] b) {
		update(b, 0, b.length);
	}

	public void update(byte[] b, int off, int len) {
		if (b == null) {
			throw new NullPointerException();
		}
		if (off < 0 || len < 0 || off > b.length - len) {
			throw new ArrayIndexOutOfBoundsException();
		}
		int crc = 0x0000;
		for (int i = off; i < off + len; i++) {
			crc = (crc >>> 8) ^ table[(crc ^ b[i]) & 0xff];
		}
		this.crc = crc;
	}

	public static void main(String[] args) {
		int a = 0xff;
		int left = a << 1; // 除2
		int right = a >>> 1; // 乘2
		System.out.println("a = " + a);
		System.out.println("a >>> 1 = " + right + ",0x" + int2Hex(right) + ",0b" + int2Bin(right));
		System.out.println("a << 1 = " + left + ",0x" + int2Hex(left) + ",0b" + int2Bin(left));

		CRC16 crc16 = new CRC16();
		String s = " 利用CRC算出来的值，不一定要为0才能使用，不为0也一样使用的（发送端跟接收端算出来的结果一样即可）。\n" +
				"     一般，书上写的CRC参数模型初始值为全0，RefIn和RefOut为False，XorOut为全0。这样，接收端算出来的CRC结果为0。\n" +
				"      更多的参数模型，可以下载第三点，常用工具的第5个工具，此工具包含21个CRC参数模型\n";
		crc16.update(s.getBytes(Charset.forName("UTF-8")));
		int crc = crc16.getValue();
		System.out.println(crc);
		System.out.println(crc16.getTableLen());
	}

	public static String int2Bin(int num) {
		return Integer.toBinaryString(num);
	}

	public static String int2Hex(int num) {
		return Integer.toHexString(num);
	}

	public int getTableLen() {
		return table.length;
	}
}
